1. Field of the Invention
The present invention relates to memory systems, in more particularly to a multilevel memory system where information stored in the lower level is advanced to the upper level according to a logical algorithm.
2. Description of the Prior Art
With the recent decreases in costs of microprocessor systems, many applications previously done by hand or in logic circuits are now being transferred thereto. Because of limited addressing capability and input-output structure in such microprocessors, any program task which requires a large memory transfer typically entails the use of a buffer memory or accelerator memory. Such accelerator memory is normally conformed as a random access store having switching times within the switching domain of the central processor. Thus, a processor which requires memory service will first look to the buffer store in order to conserve the waiting time. Random access memory having essentially the same switching speed as the central processor is, however, still expensive and therefore only limited use thereof is possible. Storage of bulk data is still most economically performed by serial storage devices such as a serial or disc magnetic store or charge-coupled-device (CCD) semiconductor store. Thus, with more complex applications, it is this serial store that contains most of the data and instructions. Such is often referred to as the system main store. Typically, in the prior art, the transfer from such main store to the random access store was performed by either invoking some overlay routine or by periodic update. In microprocessor applications, which are characteristically quite limited in their control complexity, overlay subroutines entail a large programming task for the user. Similarly, all control techniques for swapping data between the main store and the accelerator store typically complicate the system. Thus, the programmer must necessarily be either familiar with the memory structure used in these prior art techniques or must learn the architecture of a complicated control system.
With the decrease in cost of microprocessors, there has been a recent attendant wider or more popular dissemination of these devices and personnel having the necessary learning and skill to manipulate large memory systems are less frequently available. Thus, any user technique which entails complicated memory service manipulation becomes an increasingly larger source of system errors and the decreased cost of the processing equipment is traded off, without benefit, for an increased cost of programming man hours.